Certain medical conditions, such as breast cancer, are increasingly being diagnosed with minimally invasive medical techniques. Such techniques typically involve the use of clinical imaging methods that allow visualization of interior portions of a patient's body without excessive incisions and biopsies, which can cause avoidable collateral damage to healthy tissue adjacent the affected tissue. Imaging techniques can include a variety of modalities, including, for example, X-rays, computed tomographic (“CT”) X-ray imaging, fluoroscopy, portal film imaging devices, electronic portal imaging devices, ultrasound, electrical impedance tomography (“EIT”), magnetic resonance (“MR”) imaging (“MRI”), magnetic source imaging (“MSI”), magnetic resonance spectroscopy (“MRS”), magnetic resonance angiography (“MRA”), magneto electro-encephalography (“MEG”), laser optical imaging, electric potential tomography (“EPT”), brain electrical activity mapping (“BEAM”), arterial contrast injection angiography, digital subtraction angiography, positron emission tomography (“PET”) and single photon emission computed tomography (“SPECT”).
Certain imaging modalities involve the use of radiographic markers. Radiographic markers are implantable devices that are implanted into the patient through either percutaneous injection or surgical placement procedure. Typically, radiographic markers include one or more solid objects, such as a metallic wire or ceramic beads, that are implanted individually or as a plurality of objects suspended in a gelatinous matrix, collagen, or polylactic acid. The solid objects can temporarily increase visibility of the marker to certain imaging modalities such as ultrasound imaging. The markers can be readily detected by imaging modalities and are typically shaped into an artificial shape such that the marker can be distinguished from naturally occurring anatomical structures in the patient's body. For example, the markers can have artificial shapes such as coils, stars, rectangles, spheres or other artificial shapes that do not naturally occur in anatomical structures. The markers provide a reference point or landmark for physicians to localize a biopsy or surgical site in subsequent imaging studies or to facilitate image registration during image-guided therapeutic procedures.
Certain conventional markers appear as signal voids or dark artifacts when imaged with magnetic resonance imaging. However, the dark appearance of conventional markers can be difficult to distinguish and identify when imaging certain tissue or when searching for certain medical conditions. For example, heterogeneous breast tissue ordinarily produces numerous dark artifacts when imaged with MR imaging. The numerous dark artifacts normally occurring in the heterogeneous breast tissue can make the identifying dark artifacts of the markers difficult. Certain markers produce large susceptibility artifacts under MR imaging, which can distort images when MRI and spectroscopic modalities are employed. Certain markers can incorporate an external composition or coating that produces a positive or bright signal when imaged. However, the external composition is typically bio-absorbable and begins to dissipate soon after implantation gradually reducing the effectiveness of the marker.